Selective Separation and Preconcentration of ... - ACS Publications

Subscriber access provided by READING UNIV

Article

Selective Separation and Pre-Concentration of Scandium with Mesoporous Silica Simon Giret, Yimu Hu, Nima Masoumifard, Jean-Francois Boulanger, Estelle Juère, Freddy Kleitz, and Dominic Larivière ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.7b13336 • Publication Date (Web): 28 Nov 2017 Downloaded from http://pubs.acs.org on December 2, 2017

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

ACS Applied Materials & Interfaces is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 23

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Applied Materials & Interfaces

Selective Separation and Pre-Concentration of Scandium with Mesoporous Silica Simon Giret,a,b Yimu Hu,a,b Nima Masoumifard,a,b Jean-François Boulanger,c Estelle Juère,a,b,d Freddy Kleitz,*a,b,d and Dominic Larivière*a,e

a.

Department of Chemistry, Université Laval, Quebec City, G1V 0A6, QC, Canada. Centre de Recherche sur les Matériaux Avancés (CERMA), Université Laval, Quebec City, G1V 0A6, QC, Canada. c. Département de génie des mines, de la métallurgie et des matériaux, Université Laval, Quebec City, G1V 0A6, QC, Canada. d. Department of Inorganic Chemistry – Functional Materials, Faculty of Chemistry, University of Vienna, Währinger Straße 42, 1090 Vienna, Austria. e. Centre en Catalyse et Chimie Verte (C3V), Université Laval, Quebec City, G1V 0A6, QC, Canada. b.

E-mails: [email protected]; [email protected].

ABSTRACT Separation and pre-concentration of scandium (Sc) were successfully achieved using a mesoporous silica support that showed good selectivity for this element. Unmodified mesoporous silica materials were used as an extracting medium in a solid-liquid extraction (SLE) process. Selectivity, extraction capacity, kinetic of extraction and reusability under acidic conditions were investigated. The results demonstrate the potential of unmodified mesoporous silica materials for the selective separation and pre-concentration of Sc. As no chelating ligand was grafted on the silica surface, which is often the case for most solid phase extraction medium for metal ion separation, the experimental data allow us to hypothesize that the accessible silanols on the material surface are responsible for the selective Sc extraction. This interesting feature would drastically decrease the cost of solid-liquid extraction systems by using unmodified mesoporous silica materials. Moreover, a leachate solution obtained from a real rare earth element ore was used to determine the performances of the proposed materials in a packed column configuration. The maximum Sc adsorption on the silica materials surfaces are moderates (1 mg/g) but it is balanced by a great concentration factor (more than 100 times). The extraction performances are potentially promising, both in terms of selectivity and pre-concentration, under the acidic conditions tested. Keywords: Mesoporous silica, Scandium, Separation, Pre-concentration, Solid-phase extraction, Acid pH extraction. 1 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

1. Introduction Scandium (Sc)has historically been classified as a rare earth element (REEs), together with yttrium and the Lanthanides. In Earth's crust, scandium is not rare and estimated to be the 31st most abundant element with an average crustal abundance of 22 ppm.1 However, scandium-rich deposits and minerals containing significant quantities of Sc, such as thortveitite, euxenite and gadolinite, are sparse.2,3 Sc is generally obtained as a by-product in the form of oxide from the processing of numerous ores (e.g., aluminum, cobalt, iron, molybdenum, nickel, phosphate, tantalum, tin, titanium, tungsten, uranium, zinc and zirconium).4 These ores can be considered as sustainable for exploitation if the content of Sc ranges between 0.002% and 0.005%.5 Because of its limited distribution and the difficulties associated with its production, Sc is a rare and expensive metal. For instance, in 2009, the prices of Sc oxide (Sc2O3) with a purity of 99.0% and 99.9% were US$ 900/kg and US$ 1400/kg, respectively.6 Recently, in September 2016, the price of Sc oxide (99.95%) reached US$ 4200/Kg.7 Its steep price is amongst the factors that have hampered the diversification of the applications related to Sc. However, owing to its properties, Sc has been found to be an essential element in a wide variety of applications such as in optical industry,8 as alloys for aeronautic/sport equipment e.g., Al–Sc alloys (excellent properties including light weight, high strength, good thermal resistance and long durability) 9 and in aircraft engines e.g., Mg–Sc alloys (to reduce energy consumption).10 Also, Sc was identified as being a significant component of solid oxide fuel cells11,12 or for advanced catalyst applications.13 Currently, complex hydrometallurgical processes are commonly used for Sc extraction/purification, which mainly involve leaching, solvent extraction and precipitation.4 The pre-concentration and the separation steps are essential treatments prior to final precipitation since many other elements are present in greater concentration. While liquid-liquid extraction (LLE) is the most common and studied method for achieving the separation,14,15,16,17,18,19 alternative methods based on solid-liquid extraction (SLE) have recently emerged.20,21,22 The main advantages of SLE over LLE are first the elimination of a liquid organic phase, which can lead to environmental, safety and operational issues,23 secondly, the possibility of regeneration and reusability of the spent solid phase in SLE process in a large number of cycles. Considering the rising interests toward SLE processes compared to conventional LLE in mining industries,24 we have recently developed a number of novel hybrids based on mesoporous materials and studied their REEs extraction capacities. Among the materials investigated, mesoporous KIT-6 silica used as a solid support25,26 has shown interesting adsorption and transport properties owing to 2 ACS Paragon Plus Environment

Page 2 of 23

Page 3 of 23

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


its interconnected 3D pore structure. In addition, we also observed for the first time an exceptional and appealing behavior of pristine KIT-6 silica in the selective extraction of Sc. The affinity between the native non-functionalized silica and the Sc appeared to be suitably high, demanding further analyses and characterizations for a better understanding of this surprising interaction. Several studies were reported for the Sc extraction using modified porous materials in SLE method.27,28,29,30 In this paper, we investigated the selective extraction behavior of pure mesoporous silica materials for Sc. Competitive extraction experiments and extraction isotherms were performed to confirm the selective Sc extraction behavior of different silica solid phases (SBA-15, KIT-6, silica gel, β-zeolite). Additional characterizations were obtained (e.g., pH variation study, kinetics studies, passivation of surface silanols) with the objective of better understanding the interactions between Sc and the unmodified silica surface. Finally, column extraction tests in continuous extraction process using a real ore leachate were carried out to determine the applicability of these silica solid phases towards the purification of Sc.

2. Experimental section Chemicals. Poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) (Pluronic P123), 1-butanol anhydrous 99.8 % (BuOH), toluene anhydrous 99.8%, tetraethyl orthosilicate reagent grade 98 % (TEOS), 1,1,1,3,3,3-hexamethyldisilazane 99% (HMDS), tetraethylammonium hydroxide solution (TEAOH), Cab-O-Sil fumed silica and anhydrous ethanol were bought from SigmaAldrich. Hydrofluoric acid (HF, 40%), Triethylamine 99 % (Et3N) was purchased from Alfa Aesar. Hydrochloric acid (HCl, 37%) and nitric acid (HNO3, 70%), Ammonium oxalate monohydrate for analysis were purchased from Anachemia. Silica Gel 70 Å was bought from SiliCycle. All chemicals were used without further purification. Synthesis of silica solid phases. SBA-15 mesoporous silica material was synthesized according to the method reported by Choi et al.31 13.9 g of Pluronic P123, 252 g of distilled water and 7.7 g of HCl (37%) were mixed at 35 °C under vigorous stirring. After complete dissolution, 25 g of TEOS was added at once. This mixture was kept at 35 °C for 24 h followed by an aging step at 100 °C for 24 h under static conditions. The resulting solid product was slurried in an ethanol–HCl mixture, then filtered and dried for 48 h at 100 °C. For template removal, the as-synthesized silica powder was calcined at 550 °C for 2 h. Passivated SBA-15 (SBA-15-PASS) was prepared as follows: 200 mg of pristine SBA-15 was suspended in 12 mL of toluene and 1.5 mL of HMDS was added. The suspension was then stirred at room 3 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

temperature for 6 h to functionalize the external Si-OH groups. The resulting SBA-15-PASS was washed with toluene, ethanol, then filtered and dried for 48 h under vacuum at 80 °C. KIT-6 mesoporous silica materials were obtained following the procedure reported by Kleitz et al32. Briefly, 9.0 g of Pluronic P123 was dissolved in 325 g of distilled water and 17.4 g HCl (37%) was added under vigorous stirring. After complete dissolution, 9.0 g of BuOH was added. The mixture was left under stirring at 35 °C for 1 h, after which 19.35 g of TEOS was added at once to the homogeneous clear solution. The molar composition of the starting reaction mixture was TEOS/P123/HCl/H2O/BuOH = 1.0/0.017/1.83/195/1.31. This mixture was left under stirring at 35 °C for 24 h, followed by an aging step at 100 °C for 48 h under static conditions. The resulting solid product was then filtered and dried for 48 h at 100 °C. For template removal, the as-synthesized silica powder was first shortly washed in the ethanol-HCl mixture, and the resulting material was calcined at 550 °C for 2 h. Pure siliceous zeolite beta microcrystals (β-zeolite) were prepared using the ﬂuoride route, adapted from the procedure described in the literature.33,34 Cab-O-Sil fumed silica was stepwise added to a TEAOH solution (40 wt% in water) which was previously diluted with an adequate amount of distilled water. The formation of a homogeneous viscous liquid gel was ensured by pouring a small portion of the silica powder in each step followed by vigorous stirring for about 15 min until complete addition of the silica source. Hydrofluoric acid (48%) was dropped into the mixture using a 1 mL disposable plastic transfer pipet until the liquid gel was transformed into a solid-like gel. The white gel obtained was further homogenized using a plastic rod and aged overnight at room temperature in a capped bottle. The gel with a final molar composition of TEAOH/HF/SiO2/H2O = 0.55:0.55:1.0:6.0 was transferred into a 125 mL capacity Parr Teﬂon-lined stainless steel autoclave, and the crystallization was carried out through a static hydrothermal treatment at 140 °C. After 12 days, the autoclave was removed from the oven and cooled down to ambient temperature in air. The resulting product was dispersed in distilled water, filtered and washed with copious amount of distilled water. The solid product was dried for at least 12 h at 100°C in an oven. The organic template was removed by heating under air from room temperature to 550°C with a heating rate of 1°C min-1 and holding at 550°C for 6 h. Equipment and Characterization. The nitrogen adsorption-desorption isotherms were measured at 196 °C (77 K) with an Autosorb-1-MP sorption analyzer (Quantachrome Instruments, Boynton Beach, Florida, USA). All samples were outgassed at 150 °C (pure silica) or 80 °C (SBA-15-PASS) for at least 12 h before the analysis. The surface area (SBET) was determined using the Brunauer-Emmett-Teller (BET) equation in the pressure range of 0.05 ≤ P/P0 ≤ 0.20 and the pore volume (Vpore) was measured 4 ACS Paragon Plus Environment

Page 4 of 23

Page 5 of 23

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


at P/P0=0.95. The pore size distributions were calculated from either desorption or adsorption branch using the non-local density functional theory (NLDFT) method considering the sorption of N2 at -196 °C (77 K) in cylindrical pores for SBA-15 and KIT-6.35,36 Thermogravimetric analysis-differential scanning calorimetry (TGA-DSC) measurements were performed using a Netzsch STA449C thermogravimetric analyzer, under an air flow of 20 mL/min with a heating rate of 10 °C/min. 29Si magic-angle-spinning (MAS) nuclear magnetic resonance (NMR) analyses were carried out on a Bruker Advance 300 MHz spectrometer (Bruker Biospin Ltd, Milton, Ontario) at 59.6 MHz. 29Si and 45

Sc magic-angle-spinning (MAS) nuclear magnetic resonance (NMR) analyses were carried out on a

Bruker Avance 300 MHz spectrometer (Bruker Biospin Ltd, Milton, Canada) at 59.6 MHz for 29Si and 72.9 MHz for

45

Sc.

29

Si MAS NMR spectra were recorded with a spin echo sequence to avoid

instrument background with a recycle delay of 30 seconds in a 4 mm rotor spin at 9 kHz. For the 45Sc MAS experiments, the spinning frequency was 10 kHz, the recycle delay was 0.4 s, the number of scans was 790000 and the experiment lasted for 2 days and 7 hours for mesoporous silica KIT-6 saturated with Sc. The number of scans was 75000 and the experiment lasted for 19 hours for Sc(OH)3. Chemical shifts were referenced to tetramethylsilane (TMS) for 29Si and Sc(NO3)3 (0.06 M in D2O) for

45

Sc X-ray photoelectron spectroscopy (XPS) measurements were conducted on a Kratos

AXIS-ULTRA spectrometer with a monochromatic Al X-ray source operated at 300 W. Survey scans were recorded with a passing energy of 160 eV with increment steps of 1 eV. High energy resolution spectra (Sc2p) were recorded at 20 eV pass energy and step size of 0.05 eV. Transmission electron microscopy (TEM) images were taken using a Titan G2 ETEM with an accelerating voltage of 300 kV. Before the analysis, KIT-6 sample was dispersed in acetone for 5 min through ultrasonication. The solution is dropped onto a holey carbon-coated copper grid and dried in a vacuum oven for 1 h at 60 °C. Powder X-ray diffraction (XRD) patterns are obtained with a Rigaku Multiflex diffractometer using Cu Kα radiation at 40 mA and 30 kV. The XRD scanning is performed at steps of 0.02 with an accumulation time of 2 s. PXRD, TEM and BET data collected for pristine KIT-6 are presented in the ESI (Figure S6-S9) and confirmed the mesoporous nature of the KIT-6 used in this investigation. XPS and Sc NMR analysis of Sc saturated KIT-6, Sc(NO3) and Sc(OH)3 were performed in order to better understand the interaction between Sc ions and KIT-6 surface. Batch extraction studies. A solution of Sc and additional ions such as REEs (Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu), Al, Fe, Th and U in HNO3 was prepared with the desired concentration and pH. The mixed REEs solutions were prepared by the dilution of calibration standards initially at 1000ppm. The solution was stirred with an appropriate mass of solid phase support (generally 10-50 mg) for 2 h (more than the equilibrium time found by kinetic studies), the suspensions were manually shaken by hand for 30s every 10 min, after which the solution was filtered through a 0.2 5 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

µm syringe filter, this type of filters already demonstrated no REEs retention, as verified in our previous study.37 Then, a known concentration of indium was added as an internal standard in the solution. The initial and final concentrations of all the elements were determined by ICP-MS/MS (model 8800, Agilent Technologies). The optimized instrument parameters are presented in Supporting Information. The data presented are an average of triplicates. The Kd (mL/g) values were calculated by the following equation: ࡷࢊ =

࡯࢏ − ࡯ࢌ ࢂ ∗ ࡯࢏ ࢓

Where Cf and Ci (mg/L) are the final and initial concentrations, V (mL) is the volume of solution used for extraction and m (g) is the mass of solid phase used. The effect of pH on Sc extraction was measured using a solution of 1 mg/L of mixed REEs prepared at various pH (ranging from 1.6 to 4.8) adjusted with HNO3 (0.7 M) and/or NH4OH (0.1 M). For clarity purposes, only Sc extraction results are reported in this investigation for KIT-6, although all the REEs were analyzed. This experiment was performed in batch mode. The change of equilibrium pH during Sc-uptake at higher concentrations was measured. 40 mL of Sc solution at 80 ppm with initial pH of 3 was mixed with 500 mg of silica powder (KIT-6). After the equilibrium was achieved (typically after 2 h), the pH of the solution was measured before adding another 500 mg of KIT-6. The same process was repeated until the final pH of the solution stabilized. The isotherm adsorption studies were performed using three materials i.e., KIT-6, SBA-15 and Silica Gel. The pH of all solutions was adjusted to 3 (optimal pH for Sc extraction Figure 2), and Sc concentrations ranging from 1 to 25 mg/L were used to determine the maximum adsorption capacity. Kinetics studies were also performed for the following samples: KIT-6, SBA-15 and silica gel. A solution of 10 mg/L of Sc was used. The pH of the solution was adjusted to 3 and the contact time varied from 0.5 min to 4 h. Manual column extraction studies. 25 mg of materials were packed inside a column using the slurry method described elsewhere.38 The packed columns were then conditioned with 5 ml of a solution of HNO3 at pH 3. For reusability assessment with the KIT-6 material, ten sequential cycles were performed, each cycle being composed of the steps summarised in Table 1. Changes in the physicochemical parameters

6 ACS Paragon Plus Environment

Page 6 of 23

Page 7 of 23

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


derived from N2 physisorption measurements at low temperature (−196 °C) were evaluated prior and after the 10 sequential cycles (Figure S8 and S9). For extraction test with SBA-15-PASS, 5 mL of the REEs solution at 50 µg/L was passed through the column at a nominal flow rate of 1mL/min using a peristaltic pump. To strip the REEs, the adsorbent was flushed with 5 mL (NH4)2C2O4 ammonium oxalate solution (0.05 M). For each step of the manual column extraction studies, the solutions were recovered at the outlet of the channel of the column and then a known concentration of indium was added as internal standard to the solution. The initial and final concentrations of all the elements were determined by ICP-MS/MS. Automated column extraction studies. The solid phase KIT-6 (750 mg) was packed in a column cartridge, using the slurry packing technique. 38 Before the extraction test, each column was conditioned with a solution of HNO3 (pH = 3). The solution of REEs was passed through the column at a nominal flow rate of 1 mL/min using a chromatographic pump (ICS-3000 single pump, Dionex). The outlet channel of the column was connected to a mixing chamber to introduce a known concentration of indium (internal standard). The outlet channel of the mixing chamber was directly linked to the ICP-MS/MS to obtain the corresponding chromatogram. A solution of ammonium oxalate (NH4)2C2O4 was used as a recovery agent at a concentration of 0.05 M and a flow rate of 1 mL/min. After recovery, water was used as neutralization agent to remove traces of (NH4)2C2O4 solution, flow rate: 1 mL/min. A mineral leachate was prepared from a 100 kg sample originating from a prospective area located in Eastern Canada, which was crushed to 100% passing 10 mesh (1.7 mm). After homogenization, the sample was split into 1 kg lots. Then, direct ore leaching was carried out;39 100 g of crushed ore was mixed with 500 g of water and 20 g of sulphuric acid to form a slurry of 16% solids by weight. The mixture was stirred and heated at 80 °C for 24 h. The solution was filtered and oxalic acid (H2C2O4) was used for the selective precipitation of REEs.40 The solid was recovered by filtration and leached with 20 mL of diluted hot hydrochloric acid. Again, oxalic acid (H2C2O4) was used for the selective precipitation of REEs. The solid was recovered by filtration and calcined at 700 °C. Then, after calcination, the solid was leached with diluted hot hydrochloric acid before dilution using deionized water. Finally, the pH of the solution was adjusted to 3 with either HNO3 or NH4OH. This solution was used in automated column extraction and its original composition was investigated with ICP-MS/MS, the corresponding concentration is shown in Table 2. 3. Results and discussion 7 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Batch extraction studies. The preliminary findings revealed high and selective Sc uptake by the pristine KIT-6 silica material (Figure 1), the Kd for Sc was three times higher than for other REEs. Considering those data, a series of batch extraction experiments were conducted to determine the best extraction conditions. Therefore, the influence of pH on Sc extraction was investigated. This parameter is crucial since the uptake of the ion by the adsorbent is strongly affected by the pH of the solution.41 Figure 2 shows that KIT-6 exhibits a significant extraction capacity in the pH range 3 to 4.8. The maximum extraction of Sc was observed at pH close to 3, which corresponds to the point of zero zeta potential (pHiep) of pure amorphous and mesoporous silica.42, 43 At more acidic pH values, i.e., pH < 2.5, the electrostatic interactions between the Sc3+ ions and silica surface tend to be repulsive because the surface is positively charged (-OH2+). At pH close to a value corresponding to IEP, the electrostatic interactions become negligible, and the uptake of Sc is maximized. The continuing increase of Sc uptake with rising of pH from pH IEP was expected. However, we observed an unchanged Sc uptake capacity between pH 2.8 and pH 3.2. This trend can be justified with the hydrolytic chemistry of Sc and particularly the formation of the polymeric form Sc2(OH)24+ from pH 3.44,45 However, the decrease in Sc uptake at pH 4.8 may be attributed to beginning of the Sc precipitation. Since the pH variation study shows that pH 3 was optimal, we decided to keep this value for the extraction conditions in the rest of our investigations. The extraction performances of different porous silica-based solid materials were also investigated. We have selected four materials, i.e., SBA-15, KIT-6, silica gel 70 Å, which are amorphous silica with different porous structure, and a pure silica β-zeolite microcrystalline material. The porous characteristics of these materials are summarized in Table 3. Batch extraction experiments were performed, and the corresponding results are shown in Figure 3. For this study, Fe3+ and Al3+ were added with the same concentration in the initial REEs mixture as competitive agents, since they are expected to be found in large quantities in several mineral samples and mining waste and exhibit similar oxidation states to Sc. The three amorphous mesoporous sorbents exhibited selective extraction of Sc compared to REEs, although a significant portion of Fe was also extracted. Nevertheless, the uptake of Fe3+ ions might not be a severe issue, since these ions can be easily separated from solution by using straightforward hydrometallurgical techniques (mainly ionic precipitation).46 These iron removal techniques are already implemented upstream of the separation of Sc, in the REEs production industry. In addition, the uptake capacity of Fe was lower compared to Sc in column extraction studies (vide infra). SBA-15 and KIT-6 materials showed comparable extraction performances, while the silica gel extraction capacity was slightly lower (Figure 3). These three amorphous materials exhibit very close surface chemistry, therefore one can attribute the different extraction performance of the silica gel to its lower specific surface area (378.1 m2/g). β8 ACS Paragon Plus Environment

Page 8 of 23

Page 9 of 23

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


zeolite demonstrated no extraction, which can be explained by two parameters: the small micropore structure compared to the mesopores of the amorphous silica materials and the difference in surface chemistry. For the latter, it has been demonstrated that a pure silica zeolite prepared using fluoride route yields a lower number of defect sites (i.e., silanol groups) on their pore surfaces,47,48 which is a first clue of silanols implication in the Sc extraction by amorphous silica materials. For the rest of the manuscript, we have thus chosen to focus on the amorphous materials. The maximum of adsorption capacity for KIT-6, SBA-15 and Silica Gel (70 Å) was calculated from sorption isotherm experiments at pH 3. As shown in Figure 4A, the initial concentration was varied from 1 to 25 mg/L for all sorbents in order to obtain the maximum adsorption plateau during the adsorption equilibrium experiments. We used the Langmuir model, and the corresponding linear regressions are shown in Figure 4B. The Freundlich model was also tested but did not fit to our data. The maxima of adsorption capacities from the Langmuir model are summarized in Table 4. KIT-6 and SBA-15 have maximum of adsorption capacities (Qm) at 1.03 and 1.14 mg of Sc per g of material respectively, while silica gel has a Qm value of 0.55 mg/g. This trend was expected since it matches with the difference of surface area of KIT-6, SBA-15 and silica gel 70 Å. If we compare the maxima of adsorption capacities in the literature,20,21,22 1 mg/g is relatively low. However, taking into account the demonstrated selectivity for Sc at pH 3 (9-fold over the other REEs), the low-cost production of the pure mesoporous silica (considering that the surfaces were not modified with an organic chelating ligand) and the possibility to recycle the adsorbent (vide infra), we suggest that pure mesoporous silica has a potential as solid phase for the selective extraction of Sc. Kinetic studies were also performed on the three above materials. A solution of Sc at 10 mg/L was used and the contact time was varied from 0.5 min to 4 h. As shown in Figure 5A, at pH 3, the adsorption equilibrium is reached rapidly after nearly 1 h for all the materials tested, and after 30 min, the adsorption reached 80% of the maximum. We noticed that during the first 10 minutes, the kinetic of adsorption is very fast for SBA-15 and KIT-6 materials, which is essential for extraction applications. As shown in Figure 5B, a pseudo-second order model was applied to the experimental data. The linearization was performed, and it demonstrated a great fit with the experiments. The pseudo-second order model is usually considered as a chemisorption model,49 this allows us to consider Sc adsorption on the mesoporous silica material surface occurring through rather strong interactions. The batch experiments allowed us to confirm the high selectivity of pure mesoporous silica extractant for Sc among the REEs. The specific binding sites are seemingly related to silanol groups on the surface of the material, however, the binding mechanism has not yet been completely 9 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

understood. Indeed, the density of Sc adsorbed on the surface was much lower than the density of accessible silanols. In fact, the silanols density of porous silica materials is expected to be from 1 to 6 OH/nm2.50,51,52 For SBA-15, the density of accessible silanols has been estimated at 1.7 OH/nm2.52 With a surface BET of 934 m2/g, this is converted into a concentration equivalent to 2.6 mmol of silanol per gram of SBA-15, which is roughly a 100-fold higher than the Sc maximum adsorption capacity of 0.022 mmol/g (1 mg/g). This calculation may suggest that a specific conformation/environment of silanol groups would be necessary to bind with the Sc and that their density could be equal to the one of the accessible geminal silanols. As expected, the pH of the Sc solution decreased with the increasing amount of KIT-6 added, due to the release of H+ during the coordination of Sc ion with the silanol groups (Figure 6). Unlike the experimental conditions for the measurement of Sc adsorption capacity under different pH (5 mL of Sc at 1 ppm with 10 mg of KIT-6 silica), the much higher Sc content and large amount of silica in this experiment resulted in measurable pH change during the ion exchange process. For comparison, the same experimental set-up was also carried out for diluted HNO3 without Sc ions (initial pH = 3), and here, no change of equilibrium pH was observed, indicating that the decrease of pH is indeed due to the ion-exchange of H+ from silanol groups with Sc3+ ions. This study enables the calculation of the quantity of H+ released during the coordination of Sc ion with silanol groups. For 1 g of material dispersed in 40 mL, a modification of the pH from 3.0 to 2.5 is observed. This change corresponds to a release of 0.086 mmol of H+. Compared with the 0.022 mmol of Sc (1 mg) adsorbed on 1 g of KIT-6, the quantity of H+ released is almost four times higher, suggesting that one ion of Sc interacts with multiple silanol groups on the mesoporous sorbent surface. This behavior is in accordance with the reported results with inorganic titanium phosphate ion-exchangers used to selectively recovery of trace Sc from waste bauxite residue.44 To further demonstrate that it is the silanol group that contribute to the Sc adsorption, the surface properties of KIT-6 after Sc adsorption were studied via XPS. After saturation of Sc, the BE peaks of Sc2p1/2 at 408.58 and Sc2p3/2 at 403.79 eV for Sc(NO3)3 (Figure S8) were shifted to 406.94 and 402.04 eV, respectively (Figure 7), which are very close those of Sc(OH)3 (407.37 and 401.86 ev for Sc2p1/2 and Sc2p3/2, respectively, Figure S8). These results suggest that the Sc ions are most likely to link with silanol groups on the material surface. Semi-continuous column extraction studies. For all the solid phases used in a SLE method, the reusability is a crucial parameter, especially in acidic conditions (pH 3). The reusability of pure mesoporous silica material during Sc separation was examined with 10 cycles of extraction/recovery. Briefly, KIT-6 was packed in a SLE-type column and three sequential cycles were performed, each 10 ACS Paragon Plus Environment

Page 10 of 23

Page 11 of 23

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


cycle was composed of the steps summarised in Table 1. As we can see in Figure 8, the extractions are stable and close to 100% (red), which means that during each cycle, the material retains the Sc from the feeding solution (at the concentration of 1 ppm and with a volume 9 ml). We can also see that the recoveries (green) by the 3 mL of ammonium oxalate solution are close to 95% after 3 cycles. During the three first cycles, we noticed a progression of the quantities of Sc recovered (respectively 63%, 91%, 97% etc.), since the extraction remains coregarding to nstant and no trace of Sc is recovered during the washing and regeneration steps, one can assume that this increase of recovered Sc is related to a part of non-reversible adsorption. We can conclude that Sc is concentrated by a factor of nearly 3 during these experiments because the volumes of recovery solutions were 3 times lower than the volumes of the feeding solutions. Overall, the KIT-6 material is reusable at least during 10 cycles at pH 3. N2 physisorption measurements were also performed on the KIT-6 sorbent prior and after the 10 cycles and the data are reported in Figure S9, S10 and Table S2. From the obtained data, it appears that the KIT-6 sorbent demonstrates good stability in terms of porosity and structure, as no dramatic changes are detected. Obviously, isotherm shape remains similar and mesopore size and size distribution are identical. Nevertheless, it can be observed that the BET value has decreased by about 10-15%, as well as pore volume, and it seems to correspond to a difference in the adsorbed volume at low relative pressure. This observation may be correlated to an evolution of the intra-wall micropores/small mesopore upon aqueous acidic treatment.53,54 For long-term use, this progressive decrease in surface area will need to be accounted for as it will eventually result in reduced adsorption capacity. To identify the impact of the silanol accessibility on the Sc extraction, we performed a passivation of SBA-15 with HMDS, yielding a surface covered by methyl groups.55 In other words, after grafting of HMDS, a very limited number of silanols remain accessible on the surface. The characterization of SBA-15-PASS is available in the Supporting Information (thermogravimetric analysis, Figure S1) and in Table 3. For this experiment, we used semi-continuous column extraction because SBA-15-PASS is hydrophobic and the use of columns ensures an adequate contact time. SBA-15-PASS was packed in a SLE-type column, 5 mL of the REEs solution at 50 µg/L was passed through the column at a nominal flow rate of 1mL/min. Then, the adsorbent was flushed with 5 mL of a solution of (NH4)2C2O4 (0.05 M). As shown in Figure 9, the concentration of the recovery solution differs from the initial concentration of Sc used to load the column. Indeed, in contrast to the previous reusability study where 100 % of the elements were recovered, here the recovery yield is only 10%. Therefore, it can be concluded that the SBA-15-PASS did not extract Sc or other REEs, and thus confirmed the role of the accessible silanols as the selective binding sites for the Sc.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Continuous column extraction studies. First and foremost, we have confirmed that the Sc signal monitored was not originating from silicon-based interferences.56 The column containing the KIT-6 silica was connected to the ICP-MS/MS through a mixing chamber where the internal standard was added. As we can see in Figures S2, S3 and S4 (Supporting Information) the adsorption remains selective for Sc and the patterns of silicon leaching did not match with Sc extraction/recovery data. After those verifications, we have focused our experiments on a real sample solution, provided by the leaching of a real ore sample. The initial concentrations of REEs, Fe, Al, Th and U of this real solution are reported in Table 2. The extractions were performed at a nominal flow rate of 1 mL/min and the corresponding chromatograms are shown in Figures 9 and 10. The elution times were close to 7 min for all REEs, excepted for Sc, Th and Fe (simplified Sc, La and Ce extraction chromatogram Figure 10; Full chromatogram figure S5). The data corresponding to Fe signal are erratic in comparison to all the other elements tested. We believe that such data are probably plagued by variation in the amount of polyatomic interferences at m/z=56,57 which might fluctuate during the analysis period (1 h). Overall, the KIT-6 sorbent completely retains the Sc, and after more than one hour, only a small portion of Sc was slowly eluted. Once again, this experience confirms the great affinity of unmodified mesoporous silica for Sc. The last step was to recover the element trapped in the solid phase using ammonium oxalate solution ((NH4)2C2O4, 0.05 M) (simplified Sc, La and Ce recovery chromatogram Figure 11; Full chromatogram figure S6). This time, all the metals were recovered at approximately the same time, i.e., 8 min. Fe and Th seem to be slightly enriched during the recovery, but not to the same extent as Sc, which exhibited an enrichment of 11770 % compared to its original concentration. The sum of the Sc quantities recovered during the elution with ammonium oxalate was estimated and compared with the amount of Sc initially introduced in the column. The corresponding mass balance sheet has a value of 98.5% and confirms that all the Sc was removed from the column during elution with ammonium oxalate. Therefore, in addition of demonstrated enrichment of Sc in the fraction, decontamination from other elements is also expected. While Al and Fe have the lowest decontamination factor from the ions tested, (Table S1) they could be easily separated from REEs using conventional hydrometallurgical approaches (e.g., precipitation). Therefore, it can be considered that the purification of Sc from other REEs is significant. As a consequence, simple pure silica materials can be envisaged as extractant for a pre-concentration technology in the Sc production industry. Nonetheless, the best ratio between extraction capacity and material price has to be found.


Page 12 of 23

Page 13 of 23

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


4. Conclusion In this work, the selective extraction and pre-concentration of Sc using pristine mesoporous silica were studied. The results demonstrated a significant adsorption capacity, promising kinetics, suitable extraction and reusability at acidic pH using a solid support produced at relatively low cost. The importance of the presence of available silanols as the specific binding sites for Sc3+ was also highlighted. This aspect should be further investigated in order to provide a better understanding of the mechanism of adsorption. Eventually, this new insight will further help to improve extractive performances (e.g., use a material with a larger surface density of silanols). Finally, the use of these materials with real mineral leachate was demonstrated along with the high level of Sc enrichment that can be achieved and this technology may be envisaged in mining industry. Acknowledgement The authors acknowledge the National Sciences and Engineering Research Council of Canada (NSERC) for the financial support. NSERC supported this work through a Strategic Project Grant (Grant # STPGP 463032 – 14).

AUTHOR INFORMATION

Corresponding Authors *Freddy Kleitz: [email protected] *Dominic Larivière: [email protected]

ORCID

Freddy Kleitz 0000-0001-6769-4180

ASSOCIATED CONTENT

Supporting Information. Supplementary Information (SI) available: ICP-MS/MS parameters and decontamination factors, additional extraction chromatography data, thermogravimetric data of passivated mesoporous silica, low-angle XRD and TEM of KIT-6 silica, nitrogen physisorption isotherms and respective NLDFT pore size distributions of pristine and used KIT-6 sorbents, and XPS data of Sc(NO3)3 and Sc(OH)3. This material is available free of charge via the Internet at http://pubs.acs.org. 13 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 1. Distribution coefficients (Kd) of pure KIT-6 silica material for all the (REEs) at 200 µg/L, pH 4, V = 5 mL, m = 10 mg, obtained by ICP-MS/MS.


Page 14 of 23

Page 15 of 23

100 90 80

Extraction yield (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


70 60 50 40 30 20 10 0

1.6

1.9

2.3

2.8

3.2

4.8

pH

Figure 2. Extraction yield of Sc with KIT-6 material at different initial pH (i.e.; 1.6, 1.9, 2.3, 2.8, 3.2, 4.8) at 1 mg/L, V = 5 mL, m = 25 mg, obtained by ICP-MS/MS.

Figure 3. Extraction yield of Sc with different silica solid supports (i.e.; zeolite β, KIT-6, SBA-15, silica gel 70Å) at 50 µg/L for all the lanthanide elements with Al and Fe as competitive elements, pH = 3, m = 50 mg, V = 5 mL.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 4. (A) Extraction isotherms of Sc with different silica solid supports (i.e.; KIT-6, SBA-15, silica gel 70Å), pH = 3, m = 50 mg, V = 5 mL. (B) Langmuir linearization with corresponding equations.

Figure 5. (A) Kinetics study of Sc extraction with different silica solid supports (i.e.; KIT-6, SBA-15, silica gel 70Å), pH = 3, m = 50 mg, V = 5 mL. (B) Pseudo-second order linearization with corresponding equations.


Page 16 of 23

Page 17 of 23

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 6. Equilibrium change upon addition of KIT-6 silica into Sc solution (40 mL, 80 ppm) and diluted HNO3, respectively. The initial pH of both solutions is 3.

Sc2p1/2 Sc2p3/2

395

400

405

410

binding energy (ev)

Figure 7. Sc2p XPS spectrum of Sc(III) loaded KIT-6.


415


100 Sc extraction /recovery %

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 18 of 23

80 60 extraction

40

recovery 20 0 1

2

3

4

5

6

7

8

9

10

number of cycle

Figure 8. Cycles of extraction (red) and recovery (green) of Sc (1ppm, 9 mL) with KIT-6 material (25 mg) at the nominal flow rate of 1 mL/min.

Figure 9. Use of passivated SBA-15 (SBA-15-PASS) as extractant for all REEs, Flow rate 1 mL/min (5min), Ci = 50 µg/L, m = 25 mg, pH = 3. Recovery solution, ammonium oxalate 0.05 M, 1 mL/min (5 min).


Page 19 of 23

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 10. Extraction chromatogram of real sample with KIT-6 packed in column. At the nominal flow rate 1 mL/min, m = 750 mg, pH = 3.

Figure 11. Recovery chromatogram of elements from real sample using KIT6 packed in column. Ammonium oxalate, 0.05 M, at the nominal flow rate 1 mL/min, m = 750 mg, pH = 3.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 20 of 23

Table 1. Experimental set-up of each cycle in reusability assessment using semi-continuous column. Steps

Duration (min)

Flow (mL/min)

Extraction

3x3

1

Recovery

3

1

Washing Regeneration

3 3

1 1

Conditions Ci = 50 µg/L of Sc, pH 3 Ammonium oxalate 0.05 M Nano-pure water HNO3, pH 4

Table 2. Initial concentration of REEs, Fe and Al of the real solution obtained by ICP-MS/MS. 27

Real initial (µg/L)

7.2 147

Real initial (µg/L) Real initial (µg/L)

Al

Sm

45

Sc

4.7 153

Eu

274.5

15.3

172

175

Yb

17.0

56

Fe

32.9 157

Gd

183.0

89

Y

116.2 159

Tb

19.4

139

La

1910.4 163

Dy

81.1

140

141

Ce

5004.5 165

Ho

12.0

Pr

146

Nd

498.5

1835.6

166

169

Er

28.9

Tm

3.0

Lu

2.0

Table 3. Surface characterization parameters calculated from nitrogen sorption.

KIT-6 SBA-15 Silica gel zeolite β SBA-15-pass

BET surface (m2/g) 850.1 933.9 378.1 673.4 428.9

Pore volume (cm3/g) 1.22 1.15 0.99 0.33 0.65

Pore size (nm) 7.6 7.7 9.2 to 15.0 0.7 7.0

Table 4. Langmuir model parameters models calculated from adsorption isotherm.

KIT-6 SBA-15 Silica gel

KL (L/mg)

Qm (mg/g)

R2

8.8481 2.5868 3.8981

1.0318 1.1367 0.5531

0.9992 0.9997 0.9946


Page 21 of 23

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


References

1 Hedrick, J. B. Rare earths, U.S. Geological Survey Minerals Yearbook, 2007. 2 Kristiansen, R. Scandium — Mineraler I Norge. Stein, 2003, 14–23. http://www.nags.net/Stein/2003/Sc-minerals.pdf. 3 Von Knorring, O.; Condliffe, E. Mineralized pegmatites in Africa. Geol. J. 1987, 22, 253–270. 4 Wang, W.; Pranolo, Y.; Cheng, C. Y. Metallurgical processes for scandium recovery from various resources: A review. Hydrometallurgy. 2011, 108, 100–108. 5 Shaoquan, X.; Suqing, L. Review of the extractive metallurgy of scandium in China (1978–1991). Hydrometallurgy. 1996, 42, 337-343. 6 Hedrick, J.B. In U.S. geological survey, Mineral Commodity Summaries, 2010; Scandium, pp 140–141. 7 MineralPrices.com, Heavy rare earth metals, 2017 [Online]http://mineralprices.com. 8 Sigrist, M.; Chassaing, G.; François, J.C.; Antonangeli, F.; Zema, N.; Piacentini, M. Optical properties of scandium thin films. Phys. Rev. B. 1987, 35, 3760. 9 Ahmad, Z. The Properties and application of scandium-reinforced aluminum. JOM. 2003, 55, 35–39. 10 Shalomeev, V.A.; Lysenko, N.A.; Tsivirko, E.I.; Lukinov, V.V.; Klochikhin, V.V. Structure and properties of magnesium alloys with scandium. Met. Sci. Heat Treat. 2008, 50 (1–2), 34–37. 11 M. Akiyama, M. Japan Patent. 116026, 1994. 12 Chen, G.; Wang, Y.; Sunarso, J.; Liang, F.; Wang, H. A new scandium and niobium Co-doped cobalt-free perovskite cathode for Intermediate-temperature solid oxide fuel cells. Energy. 2016, 95, 137-143. 13 Perles, J.; Snejko, N.; Iglesias, M.; Monge, M.Á. 3D scandium and yttrium arenedisulfonate MOF materials as highly thermally stable bifunctional heterogeneous catalysts. J. Mater. Chem. 2009, 19, 6504-6511. 14 Wang, W.; Cheng, C.Y. Separation and purification of scandium by solvent extraction and related technologies: A review. J. Chem. Technol. Biotechnol. 2011, 6, 1237-1246. 15 Zhao, Z.; Baba, Y.; Kubota, F.; Kamiya, N.; Goto, M. Synergistic, Extraction of rare-earth metals and separation of scandium using 2-Thenoyltrifluoroacetone and tri-n-octylphosphine oxide in an ionic liquid system. J. Chem. Eng. Jpn. 2014, 47, 656-662. 16 Bo, Q.; Lu, J.; Li, d.; Zhang, X.; Ye, W. Extraction separation and mechanism of scandium by sec-octylphenoxy acetic acid from other rare earth elements. Chin. J. Anal. Chem. 2001, 28, 45-48. 17 Karve, M.; Vaidya, B. Selective separation of scandium(III) and yttrium(III) from other rare earth elements using cyanex302 as an extractant. Sep. Sci. Technol. 2008, 43, 1111-1123. 18 Li, D.; Wang, C. Solvent extraction of scandium(III) by cyanex 923 and cyanex 925. Hydrometallurgy. 1998, 48,301-312. 19 Sun, X.; Wu, D.; Chen, J.; Li, D. Separation of scandium(III) from lanthanides(III) with room temperature ionic liquid based extraction containing cyanex 925. J. Chem. Technol. Biotechnol. 2007, 82, 267-272. 20 Kalyan, Y.; Das, S.; Pandey, A. K.; Naidu, G. R. K.; Sharma, P. K.; Reddy, A. V. R. Solid phase preconcentration and determination of mercury and uranyl ions using an itaconic acid functionalized adsorptive membrane. Anal. Methods. 2011, 3, 2017-2024. 21 Liu, J.; Yang, X.; Cheng, X.; Peng, Y.; Chen, H. Synthesis and application of ion-imprinted polymer particles for solid-phase extraction and determination of trace scandium by ICP-MS in different matrices. Anal. Methods. 2013, 5, 1811-1817. 22 Tu, Z.; Hu, Z.; Chang, X.; Zhang, L.; He, Q.; Shi, J.; Gao, R.; Silica gel modified with 1-(2-aminoethyl)-3-phenylurea for selective solid-phase extraction and preconcentration of Sc(III) from environmental samples. Talanta. 2010, 80, 1205-1209. 23 Rizzuto, F. Fire protection for solvent extraction plants. Plumbing Engineer. 2002, 43-50. 24 Florek, J.; Giret, S.; Juère, E.; Larivière, D.; Kleitz, F. Functionalization of mesoporous materials for lanthanide and actinide extraction. Dalton Trans. 2016, 45(38), 14832-14854. 25 Florek, J.; Chalifour, F.; Bilodeau, F.; Larivière, D.; Kleitz, F. Nanostructured hybrid materials for the selective recovery and enrichment of rare earth elements. Adv. Funct. Mater. 2014, 24(18), 2668-2676. 26 Florek, J.; Mushtaq, A.; Larivière, D.; Cantin, G.; Fontaine, F.-G.; Kleitz, F. Selective recovery of rare earth elements using chelating ligands grafted on mesoporous surfaces. RSC Adv. 2015, 5(126), 103782-103789. 27 Ma, J.; Wang, Z.; Shi, Y.; Li, Q. Synthesis and characterization of lysine-modified SBA-15 and its selective adsorption of scandium from a solution of rare earth elements. RSC Adv. 2014, 4, 41597-41604. 28 Zhang, L.; Chang, X.; Zhai, Y.; He, Q.; Huang, X.; Hu, Z.; Jiang, N. Selective solid phase extraction of trace Sc(III) from environmental samples using silica gel modified with 4-(2-morinyldiazenyl)-N-(3-(trimethylsilyl)propyl)benzamide. Anal. Chim. Acta, 2008, 629(1-2), 84-91. 29 Korovin, V.; Shestak, Y.; Pogorelov, Y.; Scandium extraction by neutral organo-phosphorus compounds supported on a porous carrier. Hydrometallurgy. 1999, 52, 1-8. 30 Korovin, V.; Shestak, Y. Scandium extraction from hydrochloric acid media by levextrel-type resins containing di-isooctyl methyl phosphonate. Hydrometallurgy. 2009, 95(3-4), 346-349. 31 Choi, M.; Heo, W.; Kleitz, F.; Ryoo, R. Facile synthesis of high quality mesoporous SBA-15 with enhanced control of the porous network connectivity and wall thickness. Chem. Commun. 2003, 1340-1341. 32 Kleitz, F.; Hei Choi, S.; Ryoo, R. Cubic Ia3d large mesoporous silica: synthesis and replication to platinum nanowires, carbon nanorods and carbon nanotubes. Chem. Commun. 2003, 2136-2137.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

33 Serrano, D. P.; Van Grieken, R.; Sánchez, P.; Sanz, R.; Rodrı ́guez, L. Crystallization mechanism of all-silica zeolite beta in fluoride medium. Microporous Mesoporous Mater. 2001, 46, 35-46. 34 Larlus, O.; Valtchev, V.P. Control of the morphology of all-silica BEA-type zeolite synthesized in basic media. Chem. Mater. 2005, 17, 881-886. 35 Kleitz, F.; Bérubé, F.; Guillet-Nicolas, R.; Yang, C.-M.; Thommes, M. Probing adsorption, pore condensation, and hysteresis behavior of pure fluids in three-dimensional cubic mesoporous KIT-6 silica. J. Phys. Chem. C. 2010, 114, 93449355. 36 Staub, H.; Guillet-Nicolas, R.; Even, N.; Kayser, L.; Kleitz, F.; Fontaine, F.-G. Substantiating the influence of pore surface functionalities on the stability of Grubbs catalyst in mesoporous SBA-15 silica. Chem. Eur. J. 2011, 17, 4254-4265. 37 Lefrancois Perreault, L.; Giret, S.; Gagnon, M.; Florek, J.; Larivière, D.; Kleitz, F. Functionalization of mesoporous carbon materials for selective separation of lanthanides under acidic conditions. Applied Materials & Interfaces, 2017, 9(13), 12003-12012. 38 Lebed, P. J.; Savoie, J.-D.; Florek, J.; Bilodeau, F.; Larivière, D.; Kleitz, F. Large pore mesostructured organosilicaphosphonate hybrids as highly efficient and regenerable sorbents for uranium sequestration. Chem. Mater. 2012, 24, 41664176. 39 Boulanger, J.-F.; Bazin, C.; Turgeon, K.; Whitty-Léveillé, L. Direct extraction of rare earth elements from a silicate ore. International Mineral Processing Congress 2016. Rare Earths Symposium. 2016, 1-11. 40 Dahlberg, P. S.; Noble, A. C.; Pickarts, J. T. et al. Bear lodge project canadian Ni 43-101 prefeasibility study report on the reserves and development of the bull hill mine, Wyoming. Rare Element Resources Release. 2014, 1-516. 41 Türker, A. R. Separation, preconcentration and speciation of metal ions by solid phase extraction. Separation & Purification Reviews. 2012, 41(3), 169-206. 42 Bousse, L.; Mostarshed, S.; Van Der Shoot, B.; DE Rooij, N. F.; Gimmel, P.; Gopel, W. Zeta potential measurements of Ta2O5 and SiO2 thin films. J. Colloid Interface Sci. 1991, 147, 22-32. 43 Tanga, Y.; Lianga, S.; Yua, S.; Gaoa, N.; Zhanga, J.; Guoa, H.; Wang, Y. Enhanced adsorption of humic acid on amine functionalized magnetic mesoporous composite microspheres. Colloids Surf., A. 2012, 406, 61-67. 44 Zhang , W.; Koivula, R. T.; Wiikinkoski , E. W.; Xu, J.; Hietala, S. H. O.; Lehto, J. K.; Harjula, R. O. Efficient and selective recovery of trace scandium by inorganic titanium phosphate ion-exchangers from leachates of waste bauxite residue. ACS Sustainable Chem. Eng., 2017, 5 (4), 3103–3114. 45 Horovitz C. T. Scandium its occurrence, chemistry physics, metallurgy, biology and technology, Elsevier, London, 2012. 46 Gupta, C. K.; Mukherje, T. K. Hydrometallurgy in extraction processes, Volume 1; CRC Press: Boston, 1990. 47 Serrano, D. P.; Van Grieken, R.; Sánchez, P.; Sanz, R.; Rodrı ́guez, L. Crystallization mechanism of all-silica zeolite beta in fluoride medium. Microporous Mesoporous Mater. 2001, 46, 35-46. 48 Burel, L.; Tuel, A. Nanozeolites: New strategies for designing ultra small silicalite crystals with very few framework defects. Microporous Mesoporous Mater. 2013, 174, 90-99 49 Ho, Y.; McKay, G. Pseudo-second order model for sorption processes. Process Biochem. 1999, 34(5), 451-465. 50 de Farias, R. F.; Airoldi, C. Thermogravimetry as a reliable tool to estimate the density of silanols on a silica gel Surface. J. Therm. Anal. Calorim. 1998, 53, 751-756. 51 Zhuravlev, L. T. The surface chemistry of amorphous silica. Zhuravlev model. Colloids Surf. A. 2000, 173, 1-38. 52 Ide, M.; El-Roz, M.; De Canck, E.; Vicente, A.; Planckaert, T.; Bogaerts, T.; Van Driessche, I.; Lynen, F.; Van Speybroeck, V.; Thybault-Starzyk, F.; Van Der Voort, P. Quantification of silanol sites for the most common mesoporous ordered silicas and organosilicas: Total versus accessible silanols. Phys. Chem. Chem. Phys. 2013, 15, 642. 53 Bérubé, F.; Khadhraoui, A.; Janicke, M. T.; Kleitz, F.; Kaliaguine, S. Optimizing silica synthesis for the preparation of mesoporous Ti-SBA-15 epoxidation catalysts, Ind. Eng. Chem. Res., 2010, 49 (15), 6977–6985. 54 El Mourabit, S.; Guillot, M.; Toquer, G.; Cambedouzou, J.; Goettmann, F.; Grandjean, A. Stability of mesoporous silica under acidic conditions, RSC Adv., 2012, 2, 10916-10924. 55 Crowe, L. L.; Tolbert, L. M. Silica passivation efficiency monitored by a surface-bound fluorescent dye. Langmuir. 2008, 24(16), 8541-8546. 56 Whitty-Léveillé, L.; Drouin, E.; Constantin, M.; Bazin, C.; Larivière, D. Scandium analysis in silicon-containing minerals by inductively coupled plasma tandem mass spectrometry. Spectroc. Acta B. 2016, 118, 112-118. 57 May, T. W. Wiedmeyer, R. H. A Table of Polyatomic Interferences in ICP-MS. At. Spectrosc. 1998, 19(5), 150-155.


Page 22 of 23

Page 23 of 23

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42


ACS Paragon Plus Environment

Selective Separation and Preconcentration of ... - ACS Publications

Recommend Documents